Constant speed drive for magnetic



Jan. 31, 1950 M. CAMRAS CONSTANT SPEED DRIVE FOR MAGNETIC RECORDERS 2 Shets-Sheet 1 V /Z W Original Filed Oct. l4, 1942 'Jan. 31, 1950 M. CAMRAS CONSTANT SPEED DRIVE FOR MAGNETIC RECORDERS 2 Sheets-Sheet 2 Original Filed Oct. 14, 1942 Reissued Jan. 31, 1950 CONSTANT SPEED DRIVE FOR MAGNETIC RECORDERS Marvin Camras, Chicago, Ill., assignor to Armour Research Foundation of Illinois Institute of Technology, a corporation of Illinois Original No. 2,372,810, dated April 3, 1945, Serial No.'461,941, October 14, 1942. Application for reissue January 12, 1949, Serial No. 70,568

7 Claims.

Matter enclosed in heavy brackets appears in the original patent butiorms no part of this reissue specification; matter printed in italics indicates the additions made'by reissue This invention relates to improvements in a constant speed drive for a magnetic recorder, wherein reproduction of sound is made upon a wire, tape, or similar elongated member and magnetizes the member as it travels in accordance with the varying sound waves emanating from voices or instruments during lectures, plays, concerts, or various other types of productions.

While the instant invention is highly desirable for use in connection with magnetic recording devices of a very high fidelity type, it will be appreciated that the invention may also be used with such recording devices giving lesser fidelity and still provide a great advantage by its use.

In magnetic recording instruments utilizing a wire upon which a recording is made, the paramagnetic wire is usually of a size approximating a human hair, and this wire is customarily Wound back and forth betweena pair of reels. The wire will travel in one direction during a recording;

and is rewound in the reverse direction, and again travels forward during the reproduction of that recording. If there is any over-run, unexpected variance in speed, or slippage of the wire during its travel, the recording is adversely affected, or, if the recording has been good, then the reproduction of that good recordin will be j adversely affected. For best reproduction results, it is necessary for the wire to travel at the same speed during a reproduction as the wire travels during the making of a recording, and if the wire travels more rapidly near the later portion of the recording than it did at first, due to variance in circumference of wire upon the reels, the same relative speed will be present during the reproducing of that recording. Over-run, slippage, or unexpected variations in speed, either during recording or reproduction of a recording, should be eliminated in order to insure fidelity.

I am aware that in the past many and various constant speed drive arrangements for an elongated fiexible member have been developed, but insofar as I am aware those drives have been developed for much heavier elements than a wire of the approximate size of a human hair, and

when dealing with such a fine article the maintenance' of constant speed and the elimination of over-run and slippage provides a difiiculty which magnifies as the traveling element becomes smaller in size.

With the foregoing in mind, it is an important object of this invention to provide a driving arrangement for a magnetic recorder utilizing an elongated recording medium of very small size,

' which driving arrangement insures the recording medium moving around at a predetermined constant speed, without any over-run, unexpected speed variances, or slipping.

It is also an object of this invention to provide a constant speed driving arrangement for a magnetic recorder, in which the driving arrangement not only maintains the speed constant during the actual recording upon a wire or other elongated element, but also tends to maintain the speed constant against overrun and slippage both before and after the actual recording.

Still another feature of this invention is the provision of a constant speed drive for a magnetic recorder which is designed not only to maintain the travel of the recording medium at a predetermined speed, without unexpected variations or slippage, but also to maintain a predetermined tension upon the recording medium at all times so as to eliminate any lost motion effect upon reversal of the recording medium.

Also a feature of this invention is the provision of a constant speed driving arrangement for a magnetic recording device, in which the driving arrangement is extremely economical, highly eflicient, can be readily incorporated in a magnetic recorder, and needs little if any attention thereafter.

While some of the more salient features, characteristics and advantages of the instant invention have been above pointed out, others will become apparent from the following disclosures, taken in conjunction with the accompanying drawings, in which:

Figure l is a fragmentary front elevational view of a magnetic recording device embodying a constant speed drive arrangement involving principles of the instant invention;

Figure 2 is a fragmentary plan sectional view taken substantially as indicated by the section line II-II of Figure 1, looking in the direction of the arrows;

Figure 3 is a fragmentary diagrammatic view of the recording medium alone, illustrating the path of travel of this medium through the conv stant speed drive arrangement of Figures 1 and Y and 2; and

Figure 4 is a fragmentary front view, similar in character and location to Figure 1, but illustrating a more economical and modified form of constant speed drive.

As shown on the drawings:

In the illustrated embodiment of this invention, there is shown a panel 5 which may be a portion of any suitable housing, .cabinet, or other supporting structure. Near one side of the panel is a pulley 6 mounted on a suitable shaft "I journaled in the panel. Likewise, near the opposite side of the panel, a similar pulley 8 is mounted on a rotatable shaft 9. A recording medium II], which in the illustrated instance is in the form of a fine round wire of paramagnetic material and approximately .004 or .005 inch in diameter, is carried on these spools and may be wound back and forth between the spools in either direction. Suitable means, not shown in the drawings, may be utilized to prevent unintentional complete winding of the wire off one of the spools.

The pulley reel 8 may be driven by any suitable means to move the wire In forwardly, that is, off reel 6 and onto reel 8. Such drive takes effect through a suitable gear H carried on a shaft l2 mounted in a suitable frame I 3 on the back of the panel 15. A slip clutch arrangement imparts a drive from shaft l2 to the aforesaid shaft 9 carrying the reel 8. This slip clutch arrangement includes a disk [4 on the inner end of the shaft [2 carrying a suitable facing l5, and a disk I6 on the inner end of the shaft 9 for engagement with the facing l5. Of course, the disk l4 and the facing l5 are slidably mounted on the shaft l2, as well as rotating with the shaft, and the clutch elements are maintained in continuous contact with each other by a suitable spring I1 or equivalent means.

The reel or spool 6 may be driven counterclockwise as viewed in Figures 1 and 2 to effect a rewinding of the wire 16 in the reverse direction, namely, off reel 8 and onto reel 6. This drive is effected from any suitable means through a gear I8 on a shaft l 9 carried in a suitable subframe 20 mounted on the back of the panel 5, and the drive is effected through a slip clutch arrangement identical with that previously described in connection with the drive from shaft I2 to reel 8.

It will be appreciated that any suitable form of driving mechanism can be utilized to actuate the gears I I and I8, and the corresponding shafts I2 and I9. One form of device for this purpose would be a suitable reversing motor so that when shaft l 2 is driven to actuate reel 8 in a clockwise direction, there is no drive on reel 6, that reel merely idling, and likewise, when reel 6 is driven positively in a counter-clockwise direction, there is no drive on reel 8, which merely idles. If, however, nothing elsewas utilized in order to move the wire from one reel to the other, slippage of the wire might occur, overrunning of the wire might occur due to the frequent stops, reversals of direction and starts, and there may be unexpected variances of speed in the wire for various reasons. This would interfere with high fidelity re.- cording and also interfere with reproduction, even though the recording may have been perfect. If slippage or unexpected variances of speed occurred both during the recording, and later during the reproduction from that recording, then the defects in high fidelity reproduction are magnified.

To this end, a constantspeed drive arrange-' ment is incorporated, and for better advantage, this drive arrangement takes effect upon the wire I6 between the-heels 6 and 8. This drive arrangement includes a suitable frame and bearing carrying structure 2 I which may be mounted on the back ofthe panel A shaft v2r extending through'the panel carries on its inner end a driving gear 23, and on its outer or front end a pulley 24 provided with a plurality of grooves, in the illustrated instance there being four grooves. This shaft may be driven in either direction by the reversing motor (not illustrated) above mentioned or any other suitable form of driving means through the gear 23. In the intermediate portion thereof, theshaft 22 carries a relatively heavy flywheel 25 to insure smooth operation.

' Mounted on thepanel 5 a distance below, preferably in vertical alignment with the aforesaid pulley 24, is another free-running single-track pulley 26 of smaller size than the pulley 24. Also mounted on the panel 5 between, the pulleys 24 and 26 is a demagnetizing or erasing head 21 and a magnetizing or recording head 28. The erasing head and the recording head are positioned in any feasible location for the wire In to pass therethrough in its travel from one reel to the other. Disposed a distance below the pulley 26, but also preferably in vertical alignment with both pulley 26 and pulley 24, is a larger pulley 21 which, in the instant illustration, is provided with a doubletrack or groove. This pulley 21, like the pulley 26, is a free-running pulley mounted on a stub-shaft in the front panel 5. I

The wire or recording medium Ill is trained over the three pulleys 24, 26 and 21 in a manner This particular travel of the wire is best illus-.

trated diagrammatically in Figure 3. It will there be seen that the wire makes a turn A around the inner groove of the driven pulley 24 and then takes a loop B around the large idler pulley 21, turns over the second groove of the driven pulley 24 as indicatedat C, then takes a shorter loop D around the smallest pulley 26, returns again around the third groove of the pulley 24 as indicated at E, takes another loop F around the second groove of the largest pulley 21, passes around the fourth groove of the pulley 24 as indicated at G, and then travels onto the reel 8. As the wire passes downwardly to the small idler pulley 26, it passes through the erasing head 21, and as it rises upwardly from this pulley 26, it passes through the recording head 28.

It will be noted that due to the larger diameter 7 of the pulley 2'| over the drivenpulley 24, the first loop B will provide a greater bight around the pulley 21, and the intermediate loop D around the idler pulley 26 which is muchsmaller in diameter than the driven pulley 24 will create a much greater bight or grab around the driven pulley 24 in that loop of the wire during which the wire travels through the erasing and recording heads 21 and 28, respectively. Following this loop, there through the erasing and recording heads. A tension is also kept upon the wire in the direction of its travel, in addition to the tension inherently placed upon the wire by virtue of'its repeated; travel around the several pulleys. As stated above, if the wire is traveling from the reel -5 tothe reel 8, the reel 8 will be driven through the gear H. The gear II and likewise the shaft l2 are preferably driven at a slightly higher rate of' speed than the driven pulley 24, thus tending to rotate the reel 8 at a rate faster than the wire is A tension is thereby being delivered to the reel. placed upon the wire between the reel 8 and the driven pulley 24, and any undue efiect from such tension is offset by the slipping of the slip clutch arrangements I4, I5 and I6;

Inthe event the wire is-traveling from the reel 8-130 the reel BQthe gear l8 and shaft [9 are like-- wise driven at a slightly faster rate of speed than the driven pulley 24 which will then be operating in the reverse direction, and the same result is obtained; When either the reel 6 or the reel Bis being driven, the other reel is idling.

In Figure 4, I have illustrated a more economical form of constant speed driving arrangement which, whileprobably not as'effective as the arrangement described in connection with Figures -1, 2 and 3, is somewhat more economical constant speed and eliminating slippage, over-' run, and unexpected variances in speed.

In the instance of Figure 4, the same front 5 panel is shown with the reels 6 and 8 mounted in the same manner. These reels are driven one ata time as above explained. Likewise, the drive shaft 22 equipped with a flywheel '25 also functions in the manner as above described. In this case, however, the shaft 22 carries on its outer end a driven pulley- 24a which need have buttwo grooves therein. The wire [0 leaves the reel 6, passes half around one of the grooves in the driven pulley 24a, returns obliquely in the reverse of its original direction, and passes over an idler pulley 29, then travels from theidler pulley 29 in a direction paralleling its original course to another idler pulley 30, passes half around the idler pulley 30, back inan obliquely reversed direction, to the other groovein the pulley 24a, and then leaves toward. thereel 8. As indicated by the small arrows adjacent the wire in Figure 4, it will 'be seen that the. wire makes a loop around the small idler pulleys 29 and 30 and criss-crosses between these idler pulleys and the driven pulley 24a, the three pulleys forming in effect a triangular path of travel. By virtue of the criss-- cross arrangement, there is created'an added grab or bight around the driven pulley both in the initial passage of the wire and the subsequent passage of the wire around this pulley which will eliminate over-run, slippage, and variances in speed. The wire may pass through the erasing head 21 and the recording head 28 in its lower horizontal line of travel between the pulleys 29 and 30. The position of the erasing head and recording head are reversed in Figure 4 from the showing in Figure 1 because it is necessary for the wire in traveling from reel 6 to reel 8 to pass through the erasing head prior to its passage through the recording head, because frequently one recording is made on top of another one, and it is essential that the first recording be removed from the wire by a demagnetization process before the-wire is magnetized for the new recording. As in the previous case, each of the reels Brand 8; when driven, tends to rotate at afaster rate than the driven pulley 240. so as to maintain a tension on the wire, which tension is prevented 7 provided novel means for'association with a magnetic recorder, which means will positively pre-- vent slippage of the recording medium, over-run, or unexpected variances in speed, the travel of the recording medium being held at an even steady rate while a' recording is being made or a reproduction is being made from a previous recording. It will be appreciated that the invention is'easilyembodied within a magnetic recorder, is

economical, highly eifective and highly durable.

and distinctly improves the fidelity of the recorderwith which it is associated.

It will be especially noted that with either of the drive arrangements shown anddescribed herein,- knots or splices in therecording medium will freely follow the prescribed course of travel without binding or snagging at any point in their travel. It should also be carefully noted that the loops of recording medium around the'constant speed arrangement are controlled as to speed entirely by the flywheel 25.

The-term loop as used herein refers to a passage of the record medium over one member, then around a second, and then back; over the first member again,,or to apassage of the recordmediam over the first member, thenover apZuraZitg of additional members successively, and then back over the first-member again.

It will, of course, be understood that various detailsof construction may be-varied through awide. range without departing from the principlesofthis inventionand it is, therefore, not the purpose: tolimitithe patent granted hereon otherwiseithan necessitated. by the scope of the appended claims.

-. I claim as. my. invention:

[1. In a magnetic recording device wherein soundis recorded by magnetizing an elongated recording medium, a=pairi of spaced reels, 5. recording. mediumaon said. reels to travel from one to the other; anda constant speed drive arrangement includinga plurality of pulleys over which said medium passes 'in itstravel from one reel to the other, said. pulleys all having their centers in alignment but being of different diameters] [2. In a. magnetic recording device wherein sound. is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recordingmediumzon said reels to travel from one to the other, and a constant speed drive arrangement including a. plurality of pulleys over which said medium passes in its travel from one reel to the other, one of said pulleys being driven and the remainder being idlers, one of said reels being driven at a faster speed than said driven pulley, said medium running from said driven pulley to said driven reel, and a slip-clutch arrangement in the drive for said reel.]

3. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, a slip-clutch driving connection for each of said reels, and a constant speed drive arrangement between said reels including a driven pulley from which said medium extends to each reel, and a series of idler pulleys with each of which and the driven pulley said medium makes a. separate loop.

[4. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, and a series of pulleys of difierent sizes between said reels, said medium passing from a certain one of said pulleys to each of said reels and forming a loop around said certain pulley and each other pulley in the series] 5. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, and a series of three pulleys of different sizes between said reels, the medium passing to'each reel from the intermediately sized pulley and making a plurality of loops around said intermediate pulley and the largest pulley and a central loop around the intermediate pulley and the smallest pulley.

6. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, a series of three pulleys of difierent sizes between said reels, the medium passing to each reel from the intermediately sized pulley and making a plurality of loops around said intermediate pulley and the largest pulley and a central loop around the intermediate pulley and the smallest pulley, and recording means acting on said medium during its travel through said central loop.

7. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, a constant speed drive arrangement, including a triangular arrangement of pulleys between said reels, said medium passing around said pulleys in a manner to form a criss-cross path within the triangular formation of the pulleys.

8. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, and a constant speed drive arrangement including a plurality of pulleys over which said medium passes in its travel from one reel to the other, one of said pulleys being driven and the remainder being idlers, one of said reels being driven at a faster speed than said driven pulley, said medium running from said driven pulley to said driven reel, a slip-clutch arrangement in the drive for said reel, said medium being wrapped around at least a portion of said driven pulley at least two successive times in passing from one reel to the other, and recording means acting on a reach of medium between said driven pulley and said idler pulley.

9. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, and a constant speed drive arrangement including a plurality of pulleys over which said medium passes in its travel from one reel to the other, one of said pulleys being driven and the remainder being idlers, one of said reels being driven at a faster speed than said driven pulley, said medium running from said driven pulley to said driven reel, a slip-clutch arrangement in the drive for said reel, said medium passing over said driven pulley then over at least one idler and then again over said driven pulley as it passes from one reel to the other, and recording means acting on a reach of medium between said idler and said driven pulley.

10. In a magnetic recording device wherein sound is recorded by magnetizing an elongated recording medium, a pair of spaced reels, a recording medium on said reels to travel from one to the other, and a constant speed drive arrangement including a plurality of pulleys over which said medium passes in its travel from one reel to the other, one of said pulleys being driven and the remainder being idlers, one of said reels being driven at a faster speed than said driven pulley, said medium running from said driven pulley to said driven reel, 11 slip-clutch arrangement in the drive for said reel, said driven pulley having a pair of laterally spaced grooves in the periphery thereof, said medium passing over said driven pulley in one of said grooves, then over at least one of said idler pulleys, and then again over said driven pulley in the other of said grooves as it passes from one reel to the other, and recording means acting on a reach of medium between said idler and said driven pulley.

MARVIN CAMRAS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,758,559 Croll May 13, 1930 1,917,509 Ybarrondo July 11, 1933 2,215,468 Herzig Sept. 24, 1940 2,251,322 Buhrendorf Aug. 5, 1941 FOREIGN PATENTS Number Country Date 645,623 France Oct. 29, 1928 

